1. Field of the Invention
The present invention relates to an apparatus and method for interrupting a stream of signatures; more particularly, the present invention relates to a signature stream interrupt having successive conveyor belts in series which can be controlled to advance their supporting surfaces at relatively different speeds and the first conveyor belt being capable of having the supporting surface vary in length.
2. Description of Related Art
Various industries, particularly the printing industry, process a plurality of sheet-like articles commonly referred to as signatures. Signatures have a major plane and a perimeter which are typically rectangular or square. The signatures leave the printing press or folding machine where they are acted upon in a signature stream. The successive signatures have a forward end and a back end referred to as a tail. The front end overlaps the tail of the succeeding signatures to form a shingled stream. In this way, a continuous stream of signatures is transferred from one operation to the next. The signatures stream can move at rapid speeds from up to 80,0000 signatures per hour.
During various operations to handle and process signatures, it is desirable to separate a plurality of signatures into discreet increments. For example, signatures coming from a printing press are typically stacked in bundles having a desired number of signatures. In order to form such stacks without impacting on the operation of the printing or folding machines, it is desirable to interrupt the flow of signatures or form a gap in the stream. The signatures can be stacked without disturbing the formation of the signature from behind the gap.
Stacking apparatus are well known in the art. Common stacking machines include horizontal stackers and vertical stackers. Horizontal stackers stack the signatures with individual signatures in a vertical position supported on an edge. The stack has a stack axis which is horizontal. Vertical stackers have a vertical stacking support which supports the major plane of the signatures. The term "vertical" is nominal, and used to indicate that a stack is formed with a stack axis vertical or at an angle to the horizontal, typically greater than 45.degree. and most commonly at 45.degree. to 75.degree..
There is disclosed in the art a wide variety of horizontal and vertical stacking machines. These machines are designed to stack sheets of paper, including "signatures". Typically, the signatures have a major plane and a perimeter and are stacked with the major planes of adjacent signatures in contact with the signature perimeters aligned. The signatures are usually rectangular shaped as they are fed from a printer or folding machine. Signatures are fed at a high rate of speed to the stacker, by a conveyor belt assembly.
Useful horizontal stackers are disclosed in U.S. Pat. Nos. 4,723,883: 4,570,535 4,245,832 and 3,378,258. Vertical stackers are also widely known and disclosed in U.S. Pat. Nos. 4,311,090; 4,372,201; 4,678,387; and 4,541,763. Stackers of interest are also disclosed in U.S. Pat. Nos. 4,398,455; 4,397,229; and 4,772,003.
Vertical stackers comprise a vertical stacking table having a vertical support wall. The vertical signature support wall extends from a feed end to a discharge end. The vertical signature support is nominally vertically, but typically at an angle of from 1.degree. to 45.degree. to the vertical. In this way the forming stack rests against the vertical support wall. The vertical stacking table has a sliding signature support fork which can translate up and down along the vertical support wall. The signature support fork can be transverse to and extending from the vertical support track. A stack is squared between the sliding signature support fork and the vertical signature support wall. There can be a feed fork assembly which supports the oncoming signatures as the stack begins to form. The forming stack is transferred from the feed fork to the primary fork. The formed stack on the primary support fork is removed to a bundling and strapping apparatus where the stack is compressed and strapped to form a bundle.
In forming the bundles it is desirable to have end boards or end plates at either longitudinal end of the stack. Apparatus to automatically insert end boards during the stacking operation are disclosed in U.S. Pat. Nos. 4,372,201; 4,311,090; and 4,554,867. Yet another approach is presented in U.S. Pat. No. 4,772,003. The state of the art has been such that the end boards are carefully fit at the ends of the stack. This is because of the rapidly moving and growing stack of signatures.
Reference is made to commonly assigned U.S. Ser. No. 07/688,039, filed Apr. 19, 1991 and hereby incorporated by reference. This patent, as well as certain of the disclosed patents, indicates that prior to stacking it is desirable to interrupt the flow of the signatures stream. This application discloses a vertical stacker in which a gapper or interrupt apparatus is located between the stacker feed conveyor system and a vertical stacker. This enables a finite number of stack of signatures to be stacked and bundled without disturbing the flow of signatures from the preceding operation.
Apparatus to interrupt the flow of signatures are known in the art and are disclosed in references such as AT 387,205; DE 2,022,045; DE 2,640,032; GB 1,102,788 and GB 1,268,895.
These references indicate a state of the art in forming gaps in moving signatures streams. Typically, a pinch roll hook or other means can be used to intercept the moving stream. The signatures ahead of the intercept proceed unencumbered while those behind the interrupt accumulate for a brief period to attain a desired gap length or time between the last signature past the interrupt or gapper and the first signature which is being interrupted.
A continuing problem with interrupting a stream of rapidly moving signatures is the bunching up of signatures in a non-uniform manner immediately behind the gapping means. The signature stream continually feeds into the gapper and loses its shingled configuration with some signatures bunching directly on top of the preceding signatures. There is always a risk that a loose signature will move past the gapper leaving one or more signatures in the gap. Such loose or stray signatures can inhibit the uniform treatment of the finite stream after the gapper. Therefore, a continual concern in interrupting the flow of a high speed signature stream is a stray signature in the gap. The high speed operations to stack the gapped stream of signatures can be disturbed.